Network computer systems generally include a plurality of geographically separated or distributed computer nodes that are configured to communicate with each other via, and are interconnected by, one or more network communications media. One conventional type of network computer system includes a network data storage subsystem that is configured to provide a centralized location in the network at which to store, and from which to retrieve data. Advantageously, by using such a storage subsystem in the network, many of the network's data storage management and control functions may be centralized at the subsystem, instead of being distributed among the network nodes.
One type of conventional network data storage subsystem, manufactured and sold by the Assignee of the subject application (hereinafter “Assignee”) under the tradename Symmetrix™ (hereinafter “the Assignee's conventional storage system”), includes a plurality of disk mass storage devices configured as one or more redundant arrays of independent (or inexpensive) disks (RAID). The disk devices are controlled by back-end I/O controllers (commonly referred to as “back end” directors) that are coupled to a shared cache memory resource in the subsystem. The cache memory resource is also coupled to a plurality of front-end I/O controllers (commonly referred to as “front end” directors). The back-end controllers are coupled to respective disk adapters that, among other things, interface the back-end controllers to bus systems (e.g., small computer system interface (SCSI) based bus systems) used to couple the disk devices to the back-end controllers. Similarly, the front-end controllers are coupled to respective host channel/network adapters that, among other things, interface the front-end controllers via channel input/output (I/O) ports to the network communications channels (e.g., Gigabit Ethernet, SCSI, Enterprise Systems Connection (ESCON), or Fibre Channel (FC) based communications channels) that couple the storage subsystem to computer nodes in the computer network external to the subsystem (commonly termed “host” computer nodes or “hosts”).
In one conventional data storage network arrangement, a standalone network switch may be interjected in the communications channels intermediate to the host adapter I/O ports and the host nodes. More specifically, the host adapter channel I/O ports may be coupled to a first set of the switch's I/O ports, and a second set of the switch's I/O ports may be coupled to the host nodes. In this conventional data storage network arrangement, if the standalone network switch is appropriately configured, the host adapters (and their associated front-end controllers) may be able to exchange data/commands via the switch with any of the host nodes.
Additionally, conventional techniques have been developed to provide enhanced reliability and availability of data stored in the data storage network. One of these techniques is a data “mirroring” technique that involves the including in the data storage network of at least one geographically separated redundant pair of network data storage systems (e.g., a redundant pair of the Assignee's conventional data storage systems). According to this data mirroring technique, the data stored in one of the storage systems (hereinafter termed a “source” storage system) in a given redundant pair of storage systems may be replicated (or “mirrored”) in the other, storage system (hereinafter termed a “target” storage system) in that redundant pair of storage systems. If one of the storage systems in a given redundant pair fails, the mirror copy of the data that was stored in the failed storage system may be obtained from the other storage system in the redundant pair.
In a given redundant pair of storage systems, the one or more logical volumes in a source storage system that are mirrored in the target storage system may be referred to as a “source device group”; similarly, in a given redundant pair, the corresponding one or more logical volumes in the target storage system that serve or mirror these one or more logical volumes in the source storage system may be referred to as a “target device group.” Such device groups may span a number of physical and/or logical volumes, and in some instances (e.g., when data striping is used), several device groups may be mapped to different portions of physical or logical volumes.
Typically, in each respective redundant pair of storage systems, the source storage system may comprise a respective dedicated adapter that may be connected by a respective logical communication link to a respective dedicated adapter comprised in the target storage system. Each such respective logic communication link may comprise two respective dedicated communication channels (e.g., FC or ESCON communication channels); one of these two respective dedicated, physical communication channels may be a respective “primary” communication channel that may support (so long as the respective primary communication channel is functioning normally) write and read operations necessary to implement data mirroring-related operations (e.g., data mirroring and recovery operations) involving the respective redundant pair of storage systems, and the other of these two respective dedicated communication channels may be a respective “secondary” or fault-tolerant communication channel that may support such write and read operations in the event of failure of the respective primary communication channel.
As stated above, in this conventional data mirroring technique, each such logical communication link requires the use of a respective pair of dedicated adapters (i.e., one respective dedicated adapter in each of the redundant storage systems connected by the link). Unfortunately, heretofore, these dedicated adapters have not been configured to perform or support data transfer and storage-related operations in addition to those required to carry out data mirroring-related operations. Also unfortunately, in the above-described types of conventional data storage network arrangements that include one or more standalone network switches, the standalone network switches have tended to be relatively expensive and complex devices that may require substantial amounts of time and effort to install, configure, manage, and maintain in the data storage network.